It depends what you are looking for.
I met my wife through eHarmony. Neither of us are religious at all, either. I think a pay site is better if you are looking for a serious relationship, as you need to be committed to be shelling out the monthly fee.
Free sites encourage you to browse around and contact people, which is fine, but I didn't find it worked as well. The people I know that use the free sites have a lot more casual encounters, not so much luck landing a serious relationship.

I met my boyfriend on OkC! He plays WoW on and off now - his character is a goblin hunter who builds evil robots masters named Dr. Willy Crabhammer (we're on a RP server) :D

Heh, I actually use OKCupid. It's okay, it certainly has it's issues but is a fairly fun place for quiz taking and other stuff. However, I have noticed most people are looking for casual encounters of 'sexy times' kind, which I am not into, so it can be hard to find people who are a bit more serious at times.

But it is great for the more alternative types! I had tried out eHarmony, and I hated the matches they gave me. It seems that just because I marked 'christian', despite my more liberal beliefs and rather unorthodox beliefs, I got pared with the super conservative kind. No lie, one guys profile said (when describing the ideal woman) "Someone who will bare my children". After I realized that 99.9% of guys that I was getting matched with were like that, I canceled rather quickly.

You tend to get what you pay for; and even sites with a nominal fee will weed out a lot of people, which, depending on what you are looking for, may be a very good thing or not.

I'm just chiming in to agree with Jon, OkCupid is awesome no matter what you're looking for. Romance? Friends? Friends with benefits? Friends with better benefits...